Field of Invention
The present invention relates to a flyback power converter and a control circuit and a control method thereof; particularly, it relates to such a flyback power converter and a control circuit and a control method thereof, wherein when the flyback power converter operates in a quasi-resonant (QR) mode, an operation of a power switch therein is adaptively adjusted according to a pulse width modulation (PWM) frequency.
Description of Related Art
Quasi-resonant (QR) mode is an operation mode for a flyback power converter to keep operating in a boundary condition of a discontinuous current mode (DCM), to prevent the flyback power converter from entering into a continuous current mode (CCM). However, when the flyback power converter operates in the QR mode, the bandwidth is reduced which causes an output ripple problem.
In view of the above, the present invention proposes a flyback power converter and a control circuit and a control method thereof, wherein when the flyback power converter operates in the QR mode, an ON period of a power switch or an operation bandwidth of an error amplifier circuit therein is adaptively adjusted according to a PWM frequency, to compensate the output ripple.